Systems which process information in the form of coded signals typically require an output device for printing information represented by the signals. Output devices of this kind are employed in connection with computers and in long distance message transmission for example. Office typewriters have also evolved into data processing systems of this type. In the so-called word processing or editing typewriters, the typist's keyboard operations generate signals which are recorded for subsequent retrieval and automatic printout.
To enable operation of a typewriter in response to electrical signals it was originally thought necessary to provide a highly modified typewriter of costly construction. More recently it has been found to be much more practical to utilize commercial office typewriters which are manufactured and sold without specialized internal mechanisms for the purpose of initiating typewriter operations in response to electrical signals. This is made possible through the use of a typewriter attachment which may be engaged with the typewriter and which, in the preferred forms, requires little or no modifications to the moving internal operating mechanisms of the typewriter.
Sensing elements of the attachment extend into the typewriter mechanism to detect print and function operations of the typewriter as initiated by a typist and to generate electrical signals which identify such operations. Actuator elements of the attachment extend into the typewriter to initiate operations in response to such electrical signals. Typewriter baseplate attachments of this kind are described in detail in U.S. Pat. No. 3,452,851 of L. Holmes, Jr., issued July 1, 1969 and entitled, TYPEWRITER BASEPLATE ENABLING MACHINE OPERATION BY AND GENERATION OF ELECTRICAL SIGNALS and in U.S. Pat. No. 3,658,161 of Lawrence Holmes, Jr., issued Apr. 25, 1972 and entitled, DATA INPUT MECHANISM FOR AN ELECTRICAL TYPEWRITER.
As heretofore constructed, attachments of this type are not able to initiate dead key print operations. In a dead key operation, printing of a character is not followed by the carriage movement to a succeeding printing space that normally accompanies the printing of a character by a typewriter. This enables a subsequent character to be printed at the same space without requiring back spacing.
Some commercial typewriters have built-in mechanism capable of dead key operation. Such built-in dead key mechanism is typically found in typewriters designed for printing in languages where constructed characters are required, such as the addition of an accent, a grave or a circumflex over a standard alphabet character. In such typewriters the dead key character key is customarily struck first so that, for example, an accent prints on the paper but the usual operation of the typewriter escapement mechanism does not occur. The alphabet character key is then struck causing the alphabet character to be printed at the same character space. The typewriter escapement actuates in the normal manner in conjunction with printing of the alphabet character.
Dead keys are not necessarily required in the typing of certain languages, such as the English language for example, and thus there is no built-in dead key mechanism in many typewriters. There are a number of circumstances, especially in connection with word processing or automatic typing operations, where dead key operation would be advantageous in English language typewriters or in others which also lack built-in mechanism for the purpose.
For example, if a line of characters is to be underscored the typist will usually type the entire line, then back space across the page and then underscore the line. In the automatic printing of such typing from stored signals, it is often better to print each character and underscore it immediately rather than to follow the original sequence of operations of the typist. Because of the problems of tracking underscoring and limitations on buffer space in computer logic design, the conventional computer technique is to print each character, back space and then print the individual underscore for that character before proceeding on to the next character.
Because of internal mechanical constraints, electrical typewriters usually use two character time periods to back space. The conventional underscore is an uppercase character. Consequently, in automatic typing the underscoring of a uppercase alphabet character has required one time period to print the letter, two time periods to back space and one time period to underscore for a total of four time periods.
Automatic underscoring of a lowercase character has been even more time consuming. An uppercase shift and a lowercase shift each require an additional time period. If a lowercase character is to be underscored then the conventional procedure, in automatic typing, is to print the lowercase character, shift to uppercase, back space, print the underscore, then shift to lowercase in preparation for printing of the next lowercase character. In this case, six time periods are required to print a single underscored character.
If the typewriter operating attachment were able to initiate a dead key operation, the time consumed in back spacing could be saved thereby significantly speeding up the printout of underscored text. If the need for case shifts in connection with underscoring were eliminated, still greater time savings could be realized.
Another problem encountered in typewriters operated by an attachment which responds to coded signals is the unavailability of any convenient means for emphasizing specific words. Typically, it is necessary to stop the automatic printout at the appropriate point and temporarily exchange the printing element of the typewriter for another which carries italic characters. This is a very time consuming and inconvenient operation if it must be done manually.
The present invention is directed to overcoming one or more of the problems as set forth above.